JP5091659B2 - X-ray diagnostic equipment - Google Patents

Description

  The present invention relates to an X-ray diagnostic apparatus having a flat panel detector (FPD), and more particularly to an X-ray diagnostic apparatus that resets an error caused by correction of sensitivity deterioration (ghost) of a flat panel detector due to incident X-rays. .

  The X-ray diagnostic apparatus irradiates a subject (living body) with X-rays, detects a two-dimensional X-ray distribution generated according to the X-ray absorption difference of each tissue of the subject with an X-ray detector, and converts it into a digital pixel value. A technique for converting and imaging is used.

  By the way, as an X-ray detector, an X-ray film or an X-ray I.D. I. (X-ray image. Intensifier) and X-ray I. I. -The TV system was used, but as an alternative to this, an X-ray diagnostic apparatus using an X-ray flat panel detector has been commercialized.

  The X-ray flat panel detector includes a detection unit that converts incident X-ray energy into a charge amount, a plurality of detection elements that are pixel units in which the charge amount converted by the detection unit is two-dimensionally arranged, and A digital value (pixel value) representing the luminance of each pixel, the charge amount corresponding to the X-ray amount detected within a certain time, mainly composed of an array unit composed of semiconductor switches that read and select the charge amount from each detection element. ) And providing a function to the user in the form of an image having biometric information.

  This X-ray flat panel detector can output an image in real time, and can be used for X-ray I.D. I. -Compared with a TV system, it is thin and light, has almost no distortion at the periphery of the field of view, has a high resolution, and can be formed into a wide planar square, and thus has many advantages that are useful for photographing a large field of view.

  However, in the above-described X-ray flat panel detector, the sensitivity deteriorates due to the incident X-ray dose, and there is a difference in sensitivity between the region where X-rays are incident and the region where X-rays are not incident due to the X-ray diaphragm that determines the field size. It is known to occur. As a result, the past X-ray incidence history appears as a sensitivity distribution, and there is a problem in that artifacts are generated on the currently displayed image.

Therefore, conventionally, in order to solve the problems as described above, the sensitivity of the detector is determined based on the experimental fact that the amount of conversion from the X-ray to the charge of the detector is changed by the incident X-ray. Degradation / recovery phenomenon is expressed by a mathematical model, the current sensitivity is always estimated using the mathematical model from the amount of X-ray incident on the detector and the elapsed time, and a correction coefficient that compensates for the sensitivity degradation is calculated. There has been proposed a method of correcting the output in real time (Patent Document 1).
JP 2003-156567 A

  By the way, the sensitivity deterioration / recovery phenomenon in the X-ray flat panel detector is not only largely dependent on the characteristics of the detection unit, but even if the X-ray is not irradiated after X-ray incidence continues, it is usually severe for several hours. It has been confirmed that it will continue for several days without recovery. This means that even if the current correction coefficient is determined using a mathematical model for the deterioration / recovery phenomenon due to past X-ray irradiation and the output of the detector is corrected based on the determination, it does not recover for several days. Since it continues, it cannot be said that all the deterioration and recovery phenomena caused by X-ray irradiation in the past have been completely corrected, and the correction error remains accumulated. Further, the correction error generated for each pixel is also integrated.

  As a result, if there is an error between the mathematical model and the actual deterioration / recovery phenomenon, the cumulative error increases as the number of times of imaging and the X-ray irradiation time increase due to the change of the visual field area, and artifacts are created. There is a problem that could be a problem.

  The present invention has been made in view of the above circumstances, and provides an X-ray diagnostic apparatus that reliably resets an error due to correction of sensitivity deterioration caused by a delay in recovery characteristics of a detector and provides a good diagnostic image to a user. For the purpose.

In order to solve the above-mentioned problem, the present invention detects a transmitted X-ray dose transmitted from a subject by receiving X-rays irradiated under a predetermined visual field size, and detects a detection region corresponding to the visual field size. An X-ray detection unit that extracts a pixel value of each pixel, and a sensitivity deterioration value of the X-ray detection unit due to incidence of the transmitted X-ray dose is calculated from the pixel value of each pixel extracted by the X-ray detection unit. In the X-ray diagnostic apparatus, ghost correction means for correcting the pixel value of each pixel using a correction coefficient obtained from the sensitivity deterioration value is provided, and an image of the subject is displayed based on the corrected pixel value. When an image including an error that can be recognized as an artifact exists in the displayed subject image, an adjustment signal converted into a predetermined adjustment width is output based on an increase / decrease instruction signal input from the operation means. , X-ray diagnostics, comprising the error adjustment means for adjusting with the same adjustment rate sensitivity degradation value for each pixel value of the detection region of the pixel values of the detection region is calculated by serial ghost correction means Device.

Further, the present invention detects the transmitted X-ray dose transmitted from the subject upon receiving X-rays irradiated under a plurality of field sizes, and sets the pixel value of each pixel in the detection region corresponding to each field size. A sensitivity deterioration value of the X-ray detection unit due to incidence of the transmitted X-ray dose is calculated from the extracted X-ray detection unit and the pixel value of each pixel of each detection region extracted by the X-ray detection unit, and the calculated sensitivity Ghost correction means for correcting the pixel value of each pixel in each detection region using a correction coefficient obtained from the deterioration value is provided, and the image of the subject is displayed based on the corrected pixel value of each detection region. In the X-ray diagnostic apparatus, when there is an image including an artifact that appears in a geometric shape according to the plurality of visual field sizes , an increase / decrease instruction signal input from the operation means for each detection region Based on An error adjustment unit is provided that outputs an adjustment signal converted into a desired adjustment width and adjusts a sensitivity deterioration value of a pixel value of each pixel in the corresponding detection area calculated by the ghost correction unit. It is a line diagnostic device.

Furthermore, the present invention detects the transmitted X-ray dose transmitted from the subject in response to X-rays irradiated under a plurality of field sizes, and sets the pixel value of each pixel in the detection region corresponding to each field size. A sensitivity deterioration value of the X-ray detection unit due to incidence of the transmitted X-ray dose is calculated from the extracted X-ray detection unit and the pixel value of each pixel of each detection region extracted by the X-ray detection unit, and the calculated sensitivity Ghost correction means for correcting the pixel value of each pixel in each detection region using a correction coefficient obtained from the deterioration value is provided, and the image of the subject is displayed based on the corrected pixel value of each detection region. in X-ray diagnostic apparatus, provided on the output side of the ghost correction means, the error adjustment unit which resets the correction errors due to the ghost correction means is provided, the error adjustment unit, it said plurality of field size Corresponding digital pixel values of each pixel of the plurality of detection areas, a plurality of boundary profiles extracting means for extracting the digital pixel values of each pixel in the two boundary of the detection area to each other is near the size of the plurality of detection areas Averaging means for removing noise by averaging for each digital pixel value of each pixel position of the boundary portion extracted by each boundary profile extracting means, and for each pixel position of the boundary portion of both detection regions from which noise has been removed An error included in the pixel value of the predetermined detection area calculated by the ghost correction means is obtained by using an adjustment coefficient representing a change tendency from a change in the pixel value and an adjustment coefficient related to a boundary portion between both detection areas. An X-ray diagnostic apparatus comprising a resetting unit.

  ADVANTAGE OF THE INVENTION According to this invention, the error by correction | amendment of the sensitivity degradation resulting from the delay of the recovery characteristic of a detector can be reset reliably, and a favorable diagnostic image can be provided to a user.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
First, prior to the description of the first embodiment, correction of sensitivity degradation in the prior art will be described with reference to FIG. 2, and it is assumed that the present invention has been realized.

  According to the description of the prior art, when a certain amount of X-rays are incident, the number of electrons generated in the photoelectric conversion film of the detection unit decreases with the incidence of X-rays. Recover to state. Therefore, the sensitivity distribution of the detection unit changes according to the past X-ray irradiation history including the X-ray aperture shape, and is displayed as an artifact in the current image, causing a misdiagnosis.

  In order to solve this problem, a ghost correction unit 100 shown in FIG. 2 is provided. Hereinafter, the grounds for providing the ghost correction unit 100 will be described.

Experimentally, the sensitivity degradation Y after an X-ray dose (X) is incident on the detector is
Y = AX (1)
It is represented by A is a deterioration coefficient.

Furthermore, when time t has elapsed after X-ray incidence, the sensitivity degradation Yt is
Yt = Y · Exp (−t / τ) (2)
It is represented by τ is a recovery coefficient. At this time, the sensitivity S is S0 as the initial sensitivity before deterioration.
S = S0 · (1-Yt) (3)
If you know that

  In addition, the ghost correction unit 100 is provided with a timer for measuring the elapsed time from the previous X-ray irradiation, and can measure the time after sensitivity deterioration due to X-ray irradiation.

  Therefore, the degradation coefficient A and the recovery coefficient τ obtained experimentally in advance are input to the ghost correction unit 100 based on the above equations. Then, when X-rays (X dose = X) are incident on the detector in a state where no X-rays have been incident in the past or X-rays are not incident for a time corresponding to sufficient recovery of sensitivity, detection is performed. An output S0 · X corresponding to the initial sensitivity S0 is obtained from the device.

At this time, sensitivity deterioration occurs under the influence of X-ray irradiation, and sensitivity deterioration Yt of the elapsed time t after X-ray irradiation is obtained from the formula (1) and the formula (2).
Yt = AX · Exp (−t / τ) (4)
On the other hand, the sensitivity St is obtained by substituting Equation (4) into Equation (3).
St = S0 · (1-AX · Exp (−t / τ)) (5)
It becomes.

Here, when the X-ray of the dose X is incident again after the elapse of time t, from the detector,
St · X = S0 · (1-AX · Exp (−t / τ)) · X (6)
Is output, and (1−AX · Exp (−t / τ)) less output can be obtained.

  Therefore, the ghost correction unit 100 calculates the sensitivity St at the elapsed time t in real time, and the sensitivity ratio (correction coefficient) S0 / St = 1/1 / from the real time output pixel value Pt. By multiplying by (1−AX · Exp (−t / τ)) = 1 / (1−Yt), when the incident X-ray dose is X, correction is made so that S0 · X is always output.

  In addition, the sensitivity deterioration which arises in X-ray irradiation again is represented by Yt + AX, and the sensitivity degradation when the time t further passes is represented by (Yt + AX) · Exp (−t / τ).

  That is, the sensitivity deterioration Yn due to the X-ray dose Xn incident at an arbitrary time tn uses the deterioration sensitivity Yn-1 at the previous (previous) time tn-1, and Yn = Yn-1 · Exp (-(tn-tn −1) / τ) + AXn. Here, there is no incidence of X-rays between tn and tn−1, and t0 is the time at startup, and Y0 = 0.

  If the correction method for the sensitivity deterioration (ghost) of the detector is expressed equivalently on the basis of the above theoretical support, the configuration of the ghost correction unit 100 as shown in FIG. 2 is obtained.

  In the figure, P (x, y) is a pixel value representing a digital luminance value which is an output of a pixel x, y with a detector, 101 is an X-ray dose converter for converting the pixel value P into an X-ray dose Xn, 102 Is a sensitivity deterioration calculation unit for calculating sensitivity deterioration Yn (= AXn, A is a deterioration coefficient) based on the current X dose Xn, and 103 holds the sensitivity deterioration caused by the X dose irradiated at the previous time n-1. 104, a timer for measuring the elapsed time t from the previous X-ray irradiation, 105, a recovery calculation unit for calculating deterioration recovery accompanying the elapsed time, and 106 multiplying the previous deterioration sensitivity by the recovery value, and the elapsed time t Sensitivity deterioration calculation unit for calculating the sensitivity deterioration Yt at the time, 107 is a correction coefficient calculation unit for obtaining a correction coefficient using the sensitivity deterioration Yt obtained by the sensitivity deterioration calculation unit 106, and 108 is a pixel value P (x, y). Multiplied by a correction factor to compensate for sensitivity degradation. A correction processing unit that performs. Reference numeral 109 denotes an addition calculation unit that adds the sensitivity deterioration Yn obtained by the sensitivity deterioration calculation unit 106 and the current sensitivity deterioration Yn obtained by the current sensitivity deterioration calculation unit 102 and stores the result in the holding unit 103 as the previous sensitivity deterioration Yn-1. It is.

  However, when sensitivity deterioration is corrected using the ghost correction unit 100 as described above, sensitivity deterioration due to incident X-rays is accumulated cumulatively before recovery as shown in FIG.

For example, when an X-ray with an X-ray amount Xn is incident at time t1 at the initial sensitivity S0, the estimated sensitivity degradation Yn ′ due to the incidence of the X-ray has a degradation error ΔYn, and the total sensitivity degradation error at time tn. Is ΔY ′,
Yn ′ = Yn + ΔYn ′ = (Yn−1 + ΔYn′−1) · Exp (− (tn−tn−1) / τ) + AXn + ΔYn (7)
It becomes. Here, if only the sensitivity degradation error is expanded,
ΔYn ′ = ΔYn + ΔYn′−1 · Exp (− (tn−tn−1) / τ)
+ ΔYn′−2 · Exp (− (tn−tn−2) / τ)
+ ... ……)… (8)
It becomes. In FIG. 3, the illustrated solid line (A) represents a change in actual sensitivity deterioration, and the illustrated dotted line (B) represents a change in estimated deterioration sensitivity including an error. Thus, it can be seen that past sensitivity degradation errors are accumulated over time.

  Therefore, the X-ray flat panel detector used in the X-ray diagnostic apparatus, when the recovery characteristic after X-ray irradiation requires a relatively long time, the past error due to the sensitivity deterioration that has not been completely recovered with time Since it accumulates, the error increases as the incidence of X-rays is repeated, and when the error becomes so large that it is visible, an artifact is created on the image, which affects the diagnosis.

  Therefore, the present invention realizes an X-ray diagnostic apparatus that is less susceptible to the influence of deterioration errors by resetting errors caused by delays in recovery characteristics after sensitivity deterioration based on correction of sensitivity deterioration as described above.

FIG. 1 is a block diagram showing an embodiment of an X-ray diagnostic apparatus according to the present invention.
This X-ray diagnostic apparatus includes an X-ray generator 2 configured by an X-ray tube 2a for irradiating a subject (a living body such as a human being or an animal) 1 with X-rays and an X-ray diaphragm 2b for determining a field size, and a top plate 3 The support body 5 is so arranged that the X-ray transmitted through the subject 1 holding the desired posture is detected and the X-ray detection unit 4 for obtaining X-ray transmission data in the detection region corresponding to the visual field size faces each other. Supported by The support 5 is rotatably held by a holding device 6 that is erected on the floor or the like.

  As the X-ray detector 4, an X-ray flat panel detector 4a is used. The X-ray flat panel detector 4a is formed so that a plurality of X-ray detection elements are arranged vertically and horizontally, for example, has a square matrix configuration and has a planar shape. Therefore, a rectangular detection surface capable of photographing even a large part of the subject can be configured, and as described above, it can be thinned and lightened, and can be photographed with high resolution with almost no distortion in the peripheral portion of the visual field.

  A specific configuration of this X-ray flat panel detector is a detection unit that converts incident X-ray energy into a charge amount, and the charge amount converted by the detection unit is detected and accumulated for each region (pixel). The X-ray detection element group and an array unit composed of a semiconductor switch or the like for selecting the X-ray detection element group and reading out the accumulated charge amount are configured.

  For example, a support arm having an arc shape is used as the support 5, but the support 5 is not limited to the illustrated form, and various types of supports or support devices known in the art are used.

The diagnostic imaging main body 7 is connected to the output side of the X-ray detector 4.
The diagnostic imaging main body unit 7 performs imaging control according to imaging conditions, such as an operation unit 11 such as a keyboard / mouse that serves as a user interface of the diagnostic imaging processing main unit 7, and a plurality of display units 12a,. The imaging control unit 13 and the image processing unit 14 are included. The plurality of display units 12a,..., 12n are provided because the user monitors images according to functions or requests.

  The imaging control unit 13 receives imaging X-ray conditions such as tube voltage, tube current, and X-ray aperture of the X-ray tube 1 from the operation unit 11 and imaging geometric conditions such as an imaging position (including an enlargement ratio) in the subject 1. In addition, an input instruction such as rotation speed, number of shots, collection rate, and other conditions is received, stored in an appropriate setting data memory (not shown), and shooting control is performed in accordance with a predetermined shooting sequence program under these conditions.

  The image processing unit 14 has 256 floors representing luminance via an amplifier (not shown) that amplifies the accumulated charge amount of each pixel collected for each collection rate set in the X-ray detection unit 4 with a required gain. An AD conversion unit 141 that converts to a tone digital pixel value, the ghost correction unit 142, the error adjustment unit 143, the image processing control unit 144, and the like shown in FIG. 2 are provided. 145 is a pixel value data memory, and 146 is an image memory.

  The error adjustment unit 143 has a function of resetting an error caused by correction of sensitivity deterioration by the ghost correction unit 142.

  As a means for resetting an error due to correction of sensitivity deterioration, the sensitivity distribution of each pixel is measured in a state where uniform X-rays are incident on the detection region of the X-ray detector 4a where sensitivity deterioration occurs. A method of resetting the sensitivity deterioration Y calculated by the ghost correction unit 142 shown in FIG. For example, there is no X-ray incidence in the past, or there has been X-ray incidence in the past, but there is no X-ray incidence to the extent that sensitivity has been sufficiently recovered after that. The pixel value obtained when the line is incident is CO, and is stored in an appropriate memory of the ghost correction unit 142.

  After that, when it is determined that the error has increased while observing the image displayed on the display unit 12a, for example, the pixel value CI at that time is acquired. , SCor / SO = C1 / CO can be used to obtain the relative sensitivity SCor / SO.

Therefore, the sensitivity deterioration Y Cor at this time is
YCor = 1-SCor / SO = 1-C1 / CO (9)
Therefore, the YCor is replaced with the sensitivity deterioration immediately before the X-ray incidence.

At this time, if the constant dose is X, the sensitivity deterioration Y after the elapse of time t after the incidence of the reset X-ray is
Y = YCorExp (−t / τ) + AX (10)
Therefore, correction is continued as before resetting.

  However, the reset means as described above has a problem that uniform X-rays need to be incident in order to reset. Since the reset X-ray needs to be incident on the detection surface with uniform X-rays, the reset X-ray cannot be irradiated while a living body having an X-ray absorption difference exists as the subject 1. This is because, for example, when an error increases during an examination and the user determines that a reset is necessary, the patient must be withdrawn and set to a state in which there is no living body, and then irradiated with X-rays. Is a big burden.

  Therefore, in the diagnostic apparatus according to the present invention, even when the X-ray transmission data of the living body that is the subject 1 is being collected using the error adjustment unit 143, the error due to the correction of the sensitivity deterioration by the ghost correction unit 142 can be reset. It is what you want to do.

Specifically, the error adjusting unit 143 is configured as shown in FIG.
Here, before explaining the configuration of the error adjustment unit 143 shown in FIG. 4, the visual field size will be explained with reference to FIG.

  In general, in an X-ray diagnostic apparatus, an X-ray diaphragm 2a is controlled in order to acquire an image by capturing an image of an examination site (specific site) of a living body at a normal imaging magnification and an enlarged imaging magnification. Set the field of view size. For example, as shown in FIG. 5, when two types of visual field sizes A and B are individually set in the detector 4a, the detector 4a expands the detection region A ′ and the examination region according to the normal visual field size A. The transmitted X-ray dose of the examination region of the subject 1 is individually detected with the detection region B ′ corresponding to the visual field size B, converted into pixel values, imaged, and displayed on the display unit 12a. In this case, based on an instruction from the operation unit 11 by the user, the imaging control unit 13 controls the X-ray diaphragm 2b so that X-rays are not exposed to portions that do not require imaging. Therefore, X-rays that have passed through the living body enter the detector 4a inside the selected field size, and no X-rays enter the detector 4a outside the field size.

  For example, if the user observes an image related to a certain examination site based on the visual field size B, the detection region B ′ within the visual field size B is deteriorated in sensitivity due to X-rays transmitted through the living body. At this time, in the prior art, the ghost correction unit 142 calculates sensitivity deterioration for each pixel value and obtains a correction coefficient to return to the initial sensitivity to perform ghost correction, but as long as there is a delay in recovery characteristics, As described with reference to FIG. 3, errors are accumulated.

  On the other hand, in the region outside the visual field size B, since X-rays are not incident, the sensitivity is maintained, the correction coefficient is almost “1”, and no error occurs. However, when the observation site is changed to be slightly expanded including the inspection site and observed with a wider field size A, the user gives an instruction from the operation unit 11 to control the X-ray diaphragm 2b and set the field size A, X-rays are irradiated. As a result, in the detection area A ′ corresponding to the visual field size A, a correction error that occurs during the observation of the image obtained with the visual field size B appears.

  In many cases, since the living body moves during observation in the detection region B ′ based on the visual field size B, the total X-ray dose incident on the inside of the detection region B ′ is made uniform, and accordingly, a correction error is also detected in the detection region. Since it is uniformized within B ′, when the field size B is changed to the field size A, only the boundary A′B ′ of the detection region B ′ is observed on the image as an artifact accompanying a correction error.

  Since the artifact displayed in the image has a geometric shape determined by the visual field size of the X-ray stop 2b, it can be easily determined as an artifact during visual observation.

  Therefore, the present invention is to reset the accumulated error due to the correction of the sensitivity deterioration by the error adjusting means based on the accumulation of the above experiments and the experimental results.

  Specifically, as shown in FIG. 4, the error adjustment means is configured by a display unit, for example, 12 a, an operation unit 11, and an error adjustment unit 143.

  The display unit 12a selects a plurality of field sizes A and B, displays an image based on each pixel value obtained when X-rays are incident, and appears in a geometric shape from the displayed image. It has a function of discriminating artifacts and urging increase / decrease in sensitivity deterioration by the operation unit 11.

  When the operation unit 11 is determined to be an artifact having a predetermined geometric shape during image observation on the display unit 12a, the operation key 11 is a dedicated key 11a with a ↑ / ↓ mark or a joystick 11b as a pointing device or an operation similar thereto. Using the key, an instruction signal for increasing or decreasing the sensitivity deterioration in the detection surface is input.

  The error adjustment unit 143 stores adjustment width data for increasing / decreasing sensitivity deterioration in the detection surface in advance, and when receiving an increase / decrease instruction signal from the operation unit 11, the error adjustment unit 143 has a uniform adjustment width according to the increase / decrease instruction signal. In the adjustment calculation unit 111 connected to the output side of the sensitivity deterioration calculation unit 106 of the ghost correction unit 142, the sensitivity deterioration Yt that is the output of the sensitivity deterioration calculation unit 106 is multiplied by the error adjustment signal. In addition, it has a function of obtaining the sensitivity deterioration Ytr in which the correction error is reset.

Next, the operation of the above X-ray diagnostic apparatus will be described.
First, the user uses the operation unit 11 to perform imaging X-ray conditions such as tube voltage, tube current, and X-ray aperture of the X-ray tube 1 and imaging geometric conditions such as an examination site (including a magnification) and rotation in the subject 1. When data such as speed, number of shots, data collection rate, and other conditions are input to the shooting control unit 13, these condition data are stored in an appropriate memory (not shown). Similarly, adjustment width data for resetting the correction error of sensitivity deterioration is set in the error adjustment unit 143 from the operation unit 11. Note that the adjustment width data can be changed according to a user instruction before the start of the inspection and any time during the inspection.

As the adjustment width data, a range to be increased / decreased in advance, for example, ± 1% is set on the assumption of normal X-ray irradiation, but for example, considering the incident X-ray dose, ± 0.5%, ± 1.0 %, ± 1.5%, or all types may be set in advance. When a plurality of types of adjustment width data are set, the user inputs an increase / decrease instruction signal together with the type designation from the operation unit 11 according to the appearance of the artifact. 2a and the X-ray aperture 2b are controlled, and the acquisition rate is set for the X-ray detector 4.

  Thereafter, after setting the subject 1 to maintain a desired posture on the top 3, a start instruction from the operation unit 11 by the user is input. The imaging control unit 13 emits X-rays from the X-ray tube 2a according to the set conditions, and performs imaging control according to a predetermined imaging sequence program.

  At this time, the X-ray flat panel detector 4a generates a charge amount corresponding to the X-ray dose transmitted through the examination site of the subject 1 by the X-ray detection elements of the respective pixels arranged in a two-dimensional matrix configuration. . At this time, each X-ray detection element is selected by a semiconductor switch constituting the array unit, charges are collected for each collection rate, and the luminance of each pixel is expressed via an amplifier (not shown) and the AD conversion unit 141. It is converted into a digital value, that is, a digital pixel value, and sent to the ghost correction unit 142.

  The ghost correction unit 142 captures the pixel values of each pixel collected from the detector 4a and stores them in the pixel value data memory 145, while the sensitivity deterioration calculation unit 102 sequentially calculates the sensitivity deterioration Yt based on the above-described equation (4). The calculated pixel value is multiplied using the correction coefficient obtained from this sensitivity deterioration, converted to a pixel value that gives an X-ray dose based on the initial sensitivity, and sent to the image processing control unit 144.

  The image processing control unit 144 stores the converted pixel value data in the display unit 12a after storing the image memory 146 so as to fit the display screen of the display unit 12a.

  Here, the user determines whether or not an artifact having an existing specific shape (geometric shape) appears while observing the image displayed on the display unit 12a. Usually, when X-rays are incident in the past, and the previous and current X-ray incidents are close in time, for example, as shown in FIG. When inspection is performed at B, artifacts associated with the correction error can be observed at the boundary A′B ′ of the detection region B ′ corresponding to the visual field size B from the recovery delay of the correction error.

  Therefore, when the user determines that the artifact is present, the sensitivity deterioration Yt at an arbitrary time t is obtained from the operation unit 11 using the dedicated key 11a with the ↑ / ↓ marks, the joystick 11b as a pointing device, or an operation key similar thereto. An instruction signal for uniformly increasing / decreasing is input to the error adjustment unit 143.

  When receiving the increase / decrease instruction signal, the error adjustment unit 143 converts the error adjustment signal into an error adjustment signal having a uniform adjustment width according to the increase / decrease instruction signal, for example, a signal of + 1.0% or −1.0%. , Input to the adjustment calculation unit 111. Here, the adjustment calculation unit 111 multiplies the sensitivity deterioration Yt that is the output of the sensitivity deterioration calculation unit 106 by the error adjustment signal, extracts the sensitivity deterioration Ytr in which the correction error is reset, and sends the sensitivity deterioration Ytr to the correction coefficient calculation unit 107. Ask for.

  As a result, the correction coefficient increases based on an error adjustment signal that increases the sensitivity deterioration Yt, for example, sensitivity deterioration Ytr multiplied by + 1.0%, and for example, the error ΔYn indicated by the dotted line generated at time t1 shown in FIG. 3 is removed. It approaches the limit of the solid line without error.

  When multiple types of adjustment width are set, an increase / decrease instruction signal is input after specifying the type of adjustment width according to the degree of artifact appearing in the image, that is, an image in which no artifact appears, that is, deterioration Adjustment is made so that an image without error due to correction is obtained.

  Therefore, according to the embodiment as described above, when X-rays are incident on the examination region of the subject 1, many of them often show artifacts only at the boundary portion of the detection region according to the field size. At this time, the problem is the ratio of the average error inside and outside the boundary, which is made more uniform than the error of the individual pixel values, and the pixels in the pixels in the detection region of the X-ray flat panel detector 4a. A sufficient effect can be expected by adjusting the adjustment range for sensitivity deterioration at a uniform ratio to the value.

  Even if an adjustment signal of ± 1.0% is given to the pixel value “0” of the detection area B ′, it becomes equal to the original pixel value “0” and the pixels in the detection area A ′. Even if ± 1.0% is given to the value, it is hardly affected, but the pixel value of the boundary portion A′B ′ has a great influence of eliminating artifacts.

  In this embodiment, since the estimated sensitivity degradation is adjusted instead of the correction coefficient, the adjustment result can be reflected in the subsequent estimation of sensitivity degradation.

  Therefore, when the user recognizes that the correction error has increased, the correction error can be adjusted easily and quickly while observing a transmission image with relatively little exposure without bothering the patient. Thus, a good diagnostic image can be provided to the user.

(Embodiment 2)
FIG. 6 is a configuration diagram of error adjusting means for explaining the second embodiment of the X-ray diagnostic apparatus according to the present invention. The entire configuration of the X-ray diagnostic apparatus is the same as that shown in FIG.
The present embodiment may have a configuration in which a mechanism for adjusting a correction error for sensitivity deterioration is provided for each visual field size.

  In the first embodiment, for example, for two types of visual field sizes, a uniform adjustment range increase / decrease adjustment signal is applied to a ghost correction unit for correction errors of sensitivity deterioration of pixel values collected from the X-ray detection unit 4. 142, for example, when X-rays are incident with three or more types of field sizes A, B, and C (not shown; the same applies hereinafter), for example, the detector 4a corresponding to the field sizes A and B Since the degree of the appearance of the artifact differs between the boundary between the detection areas A ′ and B ′ and the boundary between the detection areas B ′ and C ′ of the detector 4a corresponding to the visual field sizes B and C, the adjustment range is uniform. It is difficult to bring the correction error close to the solid line in FIG.

  Therefore, in the present embodiment, as shown in FIG. 6, when the operation unit 11 is determined as an artifact having a predetermined geometric shape during image observation on the display unit 12 a, the visual field sizes A and B are determined. , C for each of the detection areas A ′, B ′, C ′ of the detector 4a, dedicated keys 11A, 11B, 11C with ↑ / ↓ marks, or a joystick 11b that is a pointing device while designating the visual field size or An instruction signal for increasing or decreasing the sensitivity deterioration in the detection surface is input using an operation key similar to that.

  On the other hand, the ghost correction unit 142 has substantially the same configuration as that in FIG. 4, but according to the number of detection areas A ′, B ′, and C ′ between the sensitivity deterioration calculation unit 103 and the correction coefficient calculation unit 107. A number of adjustment calculation units 111a, 111b, and 111c are connected in parallel, and switches 112a, 112b, and 112c are provided on the input / output lines of the adjustment calculation units 111a, 111b, and 111c. For example, when the visual field size A is determined, for example, when an increase / decrease instruction signal is input from the imaging control unit 13 or the dedicated keys 11A, 11B, and 11C, the visual field size A corresponds to the visual field size A determined from the error adjustment unit 143, for example. In this configuration, only the switch 112a to be turned on is turned on.

  With such a configuration, in the case of the visual field size A, only the adjustment calculation unit 111a is connected to the sensitivity deterioration calculation unit 103 of the ghost correction unit 142, and detection is performed based on the detection region A ′ corresponding to the visual field size A. While observing the display image of the pixel value of each pixel, an increase / decrease instruction signal is input to the error adjustment unit 143 from the dedicated key 11A.

  The error adjustment unit 143 receives at least one type of adjustment width data for each visual field size in advance and receives an increase / decrease instruction signal from the dedicated key 11A. An adjustment signal having one adjustment width that is optimal under the instruction is selected and input to the adjustment calculation unit 111a. The adjustment calculation unit 111a multiplies the sensitivity deterioration Yt obtained at an arbitrary time t by an adjustment signal having a predetermined adjustment width, and sends the adjusted sensitivity deterioration Yt to the correction coefficient calculation unit 107.

  Therefore, according to the embodiment as described above, by providing an adjustment mechanism for each field size, sensitivity adjustment of each pixel value detected in each detection region can be sufficiently adjusted with an adjustment signal having a uniform adjustment range. However, in this embodiment, even when there are a plurality of boundaries, the error of sensitivity deterioration correction occurring in the pixel value of each detection region is individually reset and output by the adjustment signal, so that a highly accurate deterioration error can be prevented. Adjustment can be performed.

  As a result, compared to the first embodiment, it is possible to reliably provide a user with a good diagnostic image without artifacts for each image detected in each detection region.

(Embodiment 3)
FIG. 7 is a block diagram of an error adjusting unit for explaining the third embodiment of the X-ray diagnostic apparatus according to the present invention. The entire configuration of the X-ray diagnostic apparatus is the same as that shown in FIG.
In this embodiment, a plurality of visual field sizes A, B, C, and D (A, B, C, and D are not shown; hereinafter the same) are set, and detection areas A ′, B ′, In this configuration, an error adjustment unit 143 that automatically adjusts the error of correction of sensitivity deterioration of pixel values detected by C ′ and D ′ (see FIG. 8) is provided.

  In general, when observing an image related to the examination region of the subject 1, the image of the examination region of the subject 1 is displayed on the display unit 12 a while changing to a plurality of field sizes. It exists in the boundary part (A ', B'), (B ', C'), (C ', D') of detection area A ', B', C ', D' according to B, C, D . Since these visual field sizes are mostly determined for each X-ray diagnostic apparatus, the place where the artifact appears is also known in advance.

  Therefore, the error adjustment unit 143 always monitors the boundary portion of the detection area according to the visual field size, automatically detects the accumulated correction error, and based on the tendency of the correction error accumulated in each boundary portion. An adjustment signal for increasing / decreasing the correction error is extracted, and the correction error of the pixel value output from the ghost correction unit 142 is reset.

  Usually, since the image displayed on the display unit 12a has a luminance distribution reflecting the biological information, a change in the pixel value at the boundary portion of the detection area cannot be treated as a correction error as it is. Can be extracted as error information because it hardly changes rapidly near the boundary, and the error in the boundary shows a substantially uniform change tendency as described above.

  Specifically, the error adjustment unit 143 includes boundary profile extraction units 21AB, 21BC, and 21CD, an averaging / abnormal value removal unit 22, a trend correction unit 23, adjustment coefficient output units 24AB, 24BC, and 24CD. The adjustment calculation unit 25 is configured.

  The boundary profile extraction units 21AB, 21BC, and 21CD obtain pixel values of the A′B ′ boundary portion, the B′C ′ boundary portion, and the C′D ′ boundary portion from the pixel values of the detection regions that have been ghost corrected by the ghost correction unit 142. (Boundary profile) is extracted. The averaging / abnormal value removing unit 22 averages a plurality of extracted pixel values of each boundary portion. If there is an abnormal profile among the plurality of pixel values, the average / abnormal value removing unit 22 removes and averages the abnormal profiles.

  The trend correction unit 23 extracts a difference signal of sensitivity deterioration in the pixel values of the averaged boundary portions A′B ′. The adjustment coefficient output units 24AB, 24BC, and 24CD regard the difference signal of the sensitivity deterioration of the pixel values of the boundary portions A′B ′, B′C ′, and C′D ′ as an adjustment coefficient (error amount), and output the difference signal. It is sent to the error adjustment calculation unit 25.

  The error adjustment calculation unit 25 multiplies the output of the ghost correction unit 142 in a certain detection region, for example, B ′ by the adjustment coefficient of the sensitivity deterioration difference of the pixel value of each boundary portion A′B ′, and resets the correction error. Note that the adjustment coefficient output unit 24AB uses the difference signal of the sensitivity deterioration of the pixel value of each boundary portion A′B ′ as the adjustment coefficient of the detection region B ′ because the detection region B ′ already has the detection region A ′. This is because the correction error of the sensitivity deterioration of the pixel value detected by 'is included.

Next, the effect | action of the error adjustment part 143 is demonstrated using the specific example shown in FIG.
For example, the pixel values in the detection areas A ′ and B ′ of the detector 4a when the field sizes A and B are set and the field sizes A and B shown in FIG. 9 are set will be described as an example.

  It is assumed that the image detected in the detection area A ′ already contains an error due to sensitivity deterioration correction of the image value in the detection area B ′ due to X-ray incidence.

  Therefore, since the boundary profile extraction unit 21AB of the error adjustment unit 143 knows in advance the boundary A′B ′ of the detection areas A ′ and B ′, the boundary A′B ′ indicated by the oblique lines shown in FIG. A profile (pixel value) of several tens of pixels is extracted from the center line. Within this tens of pixels, it is assumed that there is little change in the biological image, and by dividing by the average value in the profile, a boundary A′B ′ representing relative sensitivity is obtained and sent to the averaging / abnormal value removal unit 22.

  The averaging / abnormal value removing unit 22 assumes that the sensitivity degradation in each of the detection areas A ′ and B ′ is uniform, and in all the profiles, the detection area A ′ and the detection area B ′ are in the boundary direction. An averaging process is performed for each pixel position, and noise included in the pixel value is removed. For example, as shown in FIG. 9B, pixel values of a plurality of scanning lines are fetched for each pixel position in the boundary direction, and an averaging process is performed for each detection area A ′ and detection area B ′ as shown in FIG. An average value obtained by removing is obtained. At this time, a profile having an abnormal change is excluded from the averaging process.

  Subsequently, the trend correction unit 23 extracts a difference in sensitivity deterioration (error amount E shown in FIG. 11) of pixel values of several pixels before and after the boundary center from the average value of the detection area A ′ and the detection area B ′. Is sent to the adjustment coefficient output unit 24AB as a trend correction signal representing the above tendency. Note that the trend correction signal representing the tendency of change may use a method such as linear approximation.

  Here, the adjustment coefficient output unit 24AB considers the trend correction signal representing the tendency of change as an adjustment coefficient (error amount E) of the detection region B ′, and sends it to the error adjustment calculation unit 25. Note that the trend signal representing the tendency of change is regarded as the adjustment coefficient for the detection region B ′. Only the detection region B ′ receives X-ray incidence under the visual field sizes A and B and causes sensitivity deterioration. This is because.

  Upon receiving the adjustment coefficient (error amount E) of the detection area B ′, the error adjustment calculation unit 25 multiplies all the correction pixel values in the detection area B ′ obtained by the ghost correction unit 142 by the adjustment coefficient and adjusts the adjustment coefficient. The pixel value is displayed on the display unit 12a via the image processing control unit 144.

  According to the embodiment as described above, with respect to the pixel values detected in each detection area under the setting of a plurality of field sizes, the average value of the boundary pixel values of two adjacent detection areas is calculated based on the amount detection area. An adjustment coefficient (error amount) that is a difference in sensitivity deterioration is extracted, and the pixel value of the detection area having a relatively large X-ray incidence with respect to a large detection area having a small X-ray incidence is detected as the adjustment coefficient (error). Therefore, the user can concentrate on the original examination or operation while looking at a good diagnostic image without taking the trouble of manually adjusting the error.

(Other embodiments)
In the third embodiment, the pixel value of the detection region having a relatively large X-ray incidence obtained by the ghost correction unit 142 is adjusted using the adjustment coefficient obtained from the boundary pixel value of two adjacent detection regions. The adjustment coefficient (error amount E) may be used to reflect the sensitivity deterioration.

  FIG. 12 is a diagram showing a configuration in which the adjustment coefficient (error amount E) is reflected in sensitivity deterioration. First, the sensitivity deterioration holding table 113 is prepared in the ghost correction unit 142, and the sensitivity deterioration Ytb, Ytc, and the pixel values detected in the detection regions B ′, C ′, and D ′ by the sensitivity deterioration calculation unit 106 in FIG. When Ytd is obtained, it is stored in the sensitivity deterioration holding table 109.

  On the other hand, the error adjustment unit 143 shown in FIG. 12 obtains an adjustment coefficient (error amount E) obtained from the boundary pixel values of two adjacent detection regions. At this time, the error adjustment calculation unit 25 uses the error amount E. 1 / E is calculated, and the sensitivity deterioration Ytb of the corresponding detection area of the sensitivity deterioration holding table 113 is multiplied to obtain the sensitivity deterioration error adjustment amount Ytb ′, and then the sensitivity deterioration Ytb of the sensitivity deterioration holding table 113 is obtained. Is replaced with the sensitivity deterioration error adjustment amount Ytb ′, and the previous sensitivity deterioration Yn = Ytb in the addition calculation unit 110 shown in FIG. 2 is utilized and reflected in the sensitivity deterioration Yn−1.

  Thereby, the error amount E obtained by the error adjustment unit 143 is uniformly multiplied by 1 / E to all pixel values in the detection region B ′ with respect to the sensitivity deterioration Yt at the time t of the ghost correction unit 142. Thus, it can be automatically reflected in the subsequent sensitivity deterioration correction.

  In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

The block diagram which shows one Embodiment of the X-ray diagnostic apparatus which concerns on this invention. The block block diagram of the conventional ghost correction | amendment part. The figure explaining accumulation | storage of the error which arises by the sensitivity degradation correction by the conventional ghost correction | amendment part. The block diagram explaining the error adjustment means containing the error adjustment part used as the principal part of one Embodiment of the X-ray diagnostic apparatus which concerns on this invention. The figure explaining the boundary of the visual field size by X-ray aperture, the detection area of the detector corresponding to each city and size, and the quantity detection area. The block diagram explaining the error adjustment means containing the error adjustment part used as the principal part of other embodiment of the X-ray diagnostic apparatus concerning this invention. The block block diagram of the error adjustment part used as the principal part of other embodiment of the X-ray diagnostic apparatus which concerns on this invention.

The block diagram which shows one Embodiment of the X-ray diagnostic apparatus which concerns on this invention.
The figure which shows each detection area | region of the detector at the time of setting several visual field size. The figure explaining the change of the pixel value of the boundary part of two detection areas, and a boundary part. FIG. 10B is an explanatory diagram for obtaining a trend correction signal representing a change tendency by dividing and averaging the pixel values of the boundary portions of the plurality of scanning lines shown in FIG. 9B. The figure explaining the error (adjustment coefficient) calculated | required from the pixel value of two detection areas. Configuration diagram for reflecting adjustment coefficient (error amount E) in sensitivity deterioration of ghost correction unit

Explanation of symbols

  1 ... subject, 2 ... X-ray generator. 2a ... X-ray tube, 2b ... X-ray diaphragm, 4 ... X-ray detector, 4a ... X-ray flat panel detector, 7 ... image diagnosis processing main body, 11 ... operation part, 12a, ..., 12n ... display part, DESCRIPTION OF SYMBOLS 13 ... Shooting control part, 14 ... Image processing part, 21AB, 21BC, 21CD ... Boundary profile extraction part, 22 ... Averaging / abnormal value removal part, 23 ... Trend correction part, 24AB, 24BC, 24CD ... Adjustment coefficient output part, 25 ... Error adjustment calculation unit, 111, 111a, 111b, 111c ... Adjustment calculation unit, 141 ... AD conversion unit, 142 ... Ghost correction unit, 143 ... Error adjustment unit, 144 ... Image processing control unit, A, B ... Field size , A ′, B ′, C ′, D ′... Detection area.

Claims (3)

X-ray detection means for detecting a transmitted X-ray dose transmitted from a subject upon receiving X-rays irradiated under a predetermined field size and extracting a pixel value of each pixel in a detection region corresponding to the field size Then, a sensitivity deterioration value of the X-ray detection means due to incidence of the transmitted X-ray dose is calculated from the pixel value of each pixel taken out by the X-ray detection means, and a correction coefficient obtained from the calculated sensitivity deterioration value is used. Ghost correction means for correcting the pixel value of each pixel, and displaying an image of the subject based on the corrected pixel value,
When an image including an error that can be recognized as an artifact exists in the displayed image of the subject, an adjustment signal converted into a predetermined adjustment width is output based on the increase / decrease instruction signal input from the operation unit, X-ray diagnosis comprising error adjustment means for adjusting the sensitivity deterioration value of the pixel value in the detection area calculated by the ghost correction means with the same adjustment rate for each pixel value in the detection area apparatus. X-ray detection means for detecting a transmitted X-ray amount transmitted from a subject upon receiving X-rays irradiated under a plurality of field sizes and extracting pixel values of each pixel in a detection region corresponding to each field size The sensitivity deterioration value of the X-ray detection means due to the incidence of the transmitted X-ray dose is calculated from the pixel value of each pixel of each detection region extracted by the X-ray detection means, and the correction obtained from the calculated sensitivity deterioration value In the X-ray diagnostic apparatus, a ghost correction unit that corrects a pixel value of each pixel in each detection region using a coefficient is provided, and an image of the subject is displayed based on the corrected pixel value in each detection region. ,
When there is an image containing artifacts that appear in a geometric shape according to the visual field size , the image is converted to the desired adjustment width based on the increase / decrease instruction signal input for each detection area from the operation means. An X-ray diagnostic apparatus comprising: an error adjusting unit that outputs the adjusted signal and adjusts the sensitivity deterioration value of the pixel value of each pixel in the corresponding detection area calculated by the ghost correcting unit. X-ray detection means for detecting a transmitted X-ray amount transmitted from a subject upon receiving X-rays irradiated under a plurality of field sizes and extracting pixel values of each pixel in a detection region corresponding to each field size The sensitivity deterioration value of the X-ray detection means due to the incidence of the transmitted X-ray dose is calculated from the pixel value of each pixel of each detection region extracted by the X-ray detection means, and the correction obtained from the calculated sensitivity deterioration value In the X-ray diagnostic apparatus, a ghost correction unit that corrects a pixel value of each pixel in each detection region using a coefficient is provided, and an image of the subject is displayed based on the corrected pixel value in each detection region. ,
Provided on the output side of the ghost correction means, an error adjustment unit for resetting the correction error by the ghost correction means,
The error adjustment unit is configured to detect each pixel at a boundary portion between two detection regions having a size close to the detection pixel from the digital pixel value of each pixel of the plurality of detection regions corresponding to each of the plurality of field sizes. A plurality of boundary profile extraction means for extracting the digital pixel values, an averaging means for averaging each digital pixel value at each pixel position of the boundary portion extracted by each boundary profile extraction means to remove noise, and noise Calculated by the ghost correcting means using means for obtaining an adjustment coefficient representing a change tendency from a change in pixel value for each pixel position of the boundary portion between both detection areas and an adjustment coefficient for the boundary portion between both detection areas. An X-ray diagnostic apparatus comprising: means for resetting an error included in a pixel value of a predetermined detection area.

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